proxy_buffers

[error] upstream sent too big header while reading response header from upstream

/etc/nginx/proxy_buffers

proxy_buffer_size    128k;
proxy_buffers    4    256k;
proxy_busy_buffers_size    256k;

location / {
        proxy_pass http://10.0.3.LXCIP;
        include proxy_params;
        include proxy_buffers;
        proxy_ignore_client_abort on;
    }

1. nginx -t
2. nginx -s reload

[warn] could not build optimal proxy_headers_hash

you should increase either 
proxy_headers_hash_max_size: 512
proxy_headers_hash_bucket_size: 64; 
ignoring proxy_headers_hash_bucket_size

vim /etc/nginx/nginx.conf

server_names_hash_bucket_size 64;
proxy_headers_hash_max_size 1024;
proxy_headers_hash_bucket_size 128;